Red Raider Gas Company (RRGC) has just acquired new oil fields with existing facilities in
North Dakota. RRGC plans to modify the facilities to increase production. A large supply of off
gas will be available due to multistage flashing of the oil from the wellheads. However, no gas
pipeline exists to transport the gas to a market. To avoid flaring all the off gas. RRGC studied
their planned power consumption and realized that power could generated that could be used
for the expansion and to sell in the field. They propose that the off gas from the separators be
used. RRGC has gas analysis. RRGC has selected GE LM2500 turbine generators. Gas turbine
vendor recommends an inlet fuel pressure of 400 psig at a temperature of 300 °F. The water
content is not to exceed 10 ppmw in the fuel gas. Turbines require 30% excess air, and thermal
efficiency of the turbine/generator combination is 30%. Recent study by RRGC recommends that
glycol dehydration be used to remove water from the off gas.
RRGC plans to install a new fuel gas compressor. The mechanical group has determined that
available compressors can be designed for 650 psig @ 450 °F before a 2nd stage is required. Each
stage requires a minimum 10% recycle. Interstage cooling is by exchange to surrounding air.
Maximum interstage cooling duty is 13 MMBtu/hr. Interstage cooler dP is 10 psi.
Questions that RRGC needs answered:

1. How much electrical power can be generated from 100 MMSCFD?
2. What is the glycol requirement to remove water from fuel gas?
3. Is the specified compressor one stage or two? What was the compressor duty (Hp) Was
   the air cooler duty below 13 MMBtu/hr?
4. What is the maximum amount of power that can be would be recovered from the gas
   turbine?
5. How much CO2 will the facility produce, lbm/yr?
6. The combustion efficiency of a flare is about 98%. In the short time scale, methane is
   about 88 times as potent as CO2 as a greenhouse gas. What is the equivalent CO2
   emission from flaring.
   Project information:
   The gas is supplied to the facility at 60 psig, 150 F, 8000 ppmw water.
   A new glycol dehydration unit will be built. The unit will use an aqueous solution of
   triethylene glycol (TEG), at 99.04 mol % TEG, to remove water via a packed column. The
   process requires 2.2 gal of TEG per lb of water removed.
   The lab reports the dry gas composition as:
   Component Mol
   Fraction
   Methane 0.8882
   Ethane 0.0679
   Propane 0.0200
   n-Butane 0.0069
   i-Butane 0.0077
   i-Pentane 0.0038
   n-Pentane 0.0018
   n-Hexane 0.0018
   n-Heptane 0.0018
   Model details
   Gas turbine: The gas turbine is to be modeled as a simple conversion reactor in which
   each fuel component undergoes complete combustion with excess air, as specified in the
   project description. Since the efficiency of the turbine/generator combination is 40%,
   The fuel to the turbine is the field gas, dried, compressed and within 5 degrees of the
   specified temperature. The air to the reactor is to be considered at atmospheric pressure,
   and at 70 F. The combustion gas leaves the reactor at 800 F, 1 atm. The duty from the
   reactor is equivalent to the work from a 100% efficient gas turbine (as an energy balance
   around a real gas turbine shows). Since the efficiency of a gas turbine is about 35%
   defining an energy stream and reporting the 30% of its value in MW gives the
   equivalent electrical work from the turbine/generator. For this preliminary estimate, no
   additional components are needed (ie no compressors for air, or expanders for exhaust
   gas) are needed.
   Drying unit: the drying unit can be modeled using a HYSYS splitter. This does not
   model the absorption chemistry of the process but just the material balance